Telephone system



y 1939- R. c. MATHES' 2,164,335

v TELEPHONE SYSTEM Filed April 13, 1938 3 Sheets-Sheet 1 I lg T ATTORNEY R. c. MATH TELEPHONE sYsTEE AT I ORNEY y 4, 1939 R. c. MATHES Q 2,164,335

4 TELEPHONE SYSTEM Filed April 13, 1938 3 Sheets-Sheet 3 Patented July 4, 1939 PATENT OFFICE TELEPHONE SYSTEM Robert C. Mathes, Maplewood, N. J., asaignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application April 13, 1938 Serial No. 201,756

6 Claims.

This invention relates to signaling and communication systems and particularly to a method and means for transmitting telephone designations from one point to another.

The objects of the invention are to simplify the acts required of subscribers and operators in initiating automatic telephone calls; to increase the speed of telephone designation transmission from one point to another and to otherwise improve automatic telephone systems.

Systems have been proposed heretofore in which the designations of called lines or trunk circuits are transmitted from one point to another by means of alternating currents of different frequencies, which singly or in combination serve to characterize the different numerals or other characters of the designation.

- According to the present invention advantages are secured over systems of the prior art by providing the substation of a telephone line with a harmonic generator and with subscriber controlled means for selecting the generated harmonics to characterize the different digits of a wanted number and cause them to be transmitted to the central oifice to control the operation of automatic switches used in extending a connection from the substation to a called line. The harmonic generator at the substation may be in the form of a toroidal coil wound upon a core of permalloy or other suitable material and may be energized by current of a fundamental frequency generated at the central ofi'ice. The toroidal coil, or kick coil, is provided with a core material of very high permeability at low magnetizing forces, but which saturates sharply at relatively low fields. The harmonic voltages which appear across the coil are therefore large and travel back to the central office where they may be separated from the fundamental frequency and caused to operate the central oflice equipment. The generated harmonics may be selected by the subscriber by including in the line circuit tuning devices such as condensers, singly or in combinations to characterize the digits of the wanted designations. These harmonics may control selectively operable filter circuits at the central omce to selectively operate the central office registors, which in turn control the selective operation of the switches used in the establishment of the desired connection.

The invention will be readily understood from the following detailed description made with reference to the accompanying drawings in which:

Fig. 1 is a schematic representation of the system embodying the features of the invention and enables one to comprehend at a glance the fundamental elements which characterize the system and their relative locations;

Fig. 2 is a block diagram illustrating how the several figures of the drawings are to be combined to form a complete system;

Fig. 3 is a schematic representation of the equipment located at a subscriber's station;

Fig. 4 discloses the central oflice switches and selective receiving circuits; and

Fig. 5 illustrates the relay register circuits which function with and are controlled by the selective receiving circuits shown in Fig. 4.

Before proceeding to the operation of the system disclosed, a description of the equipment used will be given, including the substation sending mechanism and the receiving and register circuits of the central ofiice.

The subscriber'sstation, as shown in Fig. 3, is furnished with the usual telephone set I26, 'frequency generating and selecting equipment and a transformer I62 which serves to inductively associate'the latter equipment with the line circuit during the transmission of telephone designations from the subscriber's station. The frequency generating means I00 comprises a core 99 of permalloy or other suitable material and a coil wound upon the core and connected across that section of the line associated with the winding I63 of transformer I62. Interposed between one terminal of the transformer winding I63 and a corresponding terminal 98 of the coil of generator I00 is a tuned circuit consisting of the impedance coil IOI and condenser I02. This combination is tuned to the frequency of the source 200 at the central office. From a point I03 on the coil of the harmonic generator I00 there extends a lead including the impedance coil I6I. Two pairs of tuning circuits, each comprising five separate paths are associated with the coil I6I in such a manner that one of the pairs extends from one end of the coil whereas the other pair is connected to a suitable tap on the coil I6I. Two groups of five tuning circuits are used instead of one group of ten and are connected in the manner shown for the reason that such an arrangement permits more practicable values of capacity to be assigned to the condensers which constitute the individual tuning circuits. The condensers I50, I5I, etc. are normally on open circuit with respect to the line circuit, each being associated with its respective spring contact of the keyboard sender I20. The sender I20 comprises ten keys, one for each of the characters of a telephone designation. It is to be understood that the keyand letters as generally appear on the telephone dial in common use today and the numerals and letters are to be arranged in the same combinations' employed in the present type dial. More specifically, the first key I06 will carry the numeral 1 to correspond to the digit 1 of a telephone designation; the second key I06 will bear the numeral 2 and the letters ABC; the third key I" will carry the numeral 3 and the letters DEF and so forth, thus carrying out the pattern of the present dial.

As each key' is depressed a corresponding condenser 60, 6i, etc., is connected across the lineto cause a particular frequency to be selected and transmitted to the central ofilce. Each key also controlsa common switching element for a purpose to be set forth hereinafter in greater detail. By actuating several keys in succession, eight keys for an eight digit designation, a corresponding number of different frequencies are transmitted in succession to the central office to control the equipment thereat in a manner to be described hereinafter.

A brief description will now be given of the circuits and other equipment at the central ofilce. The subscriber's lines, each of which is provided with one of the senders or transmitters shown in Fig. 1, extend to the central office and appear in line-finder switches such as the line finder F. The line finder F serves to extend a calling line through to the first selector S and a sender selector switch S-I serves to extend the calling line to one of the common central ofllce register senders such as the one shown in Figs. 4 and 5.

The common register sender includes a number of controlling relays and consists essentially of a frequency detecting and selecting mechanism and a number of relay registers. A source 200 of alternating current of suitable frequency, such as 100 cycles, is provided for supplying the subscriber's line with current to excite the substation transmitter. The alternating currents representing the designations are selected as a group by a filter I, amplified by an amplifier 202, and applied to a series of individual selective filters 203, 204, 206, etc. The number of digital registers will depend upon the size of the exchange area. It may be assumed, in the present case, that the designations in this particular -area consist of two letters and four numerical digits. The letter designations are recorded on the relay registers A and B and the numerical digits are recorded on the four relay registers, two of which, the thousands and units registers, are shown. The intermediate hundreds and tens registers will be the same as those shown and have been omitted for purposes of simplicity. The alternating currents transmitted over the subscriber's line and having frequencies representing the different designation characters are selected by the filters 203, 204, etc., and then cause the operation of the register relays to register these designation characters for further use in controlling the selective switches 8, S2 and 3-4 to complete the connection through to the called subscriber's line. For a complete understanding of the operation 'of the register relays in controlling such switches, reference may be made to Patent 1,862,549, issued June 14, 1932, to R. Raymond et al. The operation of the system will now be described and for this purpose it will be assumed that the subscriber at station I26 wishes to call the subscriber at station 208. It will be assumed further that the designation of substation 206 is AL-1234 and that the letter A is the equivalent of the numeral 2 and that the letter L is the equivalent of the numeral 6. when the subscriber at station I26 lifts his receiver to initiate the call, the line circuit is closed, and the finder F is started in operation in a well-known manner to seize the calling line. At the same time the sender selector SI becomes effective to extend the calling subscriber's line' through to an idle sender. When these operations have been completed, a circuit is closed from battery through the left-hand winding of line relay 2" in the sender, over brush 2I0, contact of spring 2 on a controlling sequence switch, thence over the brush of finder 1?, over conductor I21 of the subscriber's line through the switchhook con-- tacts, closed springs H6 and I I6, conductor I20 and returning over conductor I20, through the upper brush of finder F and sequence switch contact 2I2, brush 2I2 of sender selector S-I to ground in the sender. The sequenceswitch referred to herein may be of the type well known in automatic systems of the kind in which panel selector switches are used. The line relay 206, which isnot responsive to current from the alternating current source 200, operates in response to the fiow of direct current-in the circuit just traced and closes an obvious circuit for the slowrelease relay 2. Relay 2 closes an obvious circuit for relay 200 (Fig. 5) and the latter relay operates and extends the register operating conductor-s I through to the windings of the relays of the first code register A preparatory to the operation of these relays. At the same time a tone'is sentfrom .the tone device 2I6 to notify the calling subscriber that the central ofiice equipment is ready to receive the wanted designation.

The calling subscriber now manipulates the key I06 which characterizes the first letter A in the designationofwthe called subscriber. Key I06 actuates the common rod I3I and connects the condenser I 6I across the winding I66 of transformer I62 in series with the left-hand portion of coil I6I andthat' portion of the coil of generator I00 included between terminal 61 and tap I03. At the same time the rod I2I separates springs H6 and H6 and connects the latter to spring I I 1 to close the winding I64 of transformer I62 so that the circuit extending from the central oflice now leads by way of conductor I21, through the coil I64, conductor I 22, through the closed springs II! and II 6, conductor I26 and over conductor I 20 as previously traced. The springs II 6, II 1 and I I6 are so arranged that the continuity of the line circuit is preserved while the generator I 00 is being introduced into the line circuit. Alternating current from the source 200 flows over this circuit and through the coil of generator I00. As previously stated the current generated by the source 200 has a frequency of 100 cycles though the invention is not limited to this particular frequency. The harmonic generator I00 now being excited by the fundamental frequency of 100 cycles functions to generate the harmonics of this fundamental frequency. The condensers I60, III, I62, to I66, inclusive, are tuned to the odd harmonics F1, Fa, Fs, etc. The actuation of key I06 results in the selection of the frequency F: which is now transmitted back over the line circuit and is applied to amplifier 202 by way of filter 20I and thence to the input circuits of the several filters connected to the common circuit 2 I6. There are as many of these filters as there are keys at the subscribers station and the several filters are selectively designed to pass the frequencies corresponding to the respective keys at the substation. Therefore, the frequency F3 in the circuit 2I8 resulting from the actuation of key I08 is selectively passed by filter 204 and is excluded by all other filters connected to the calling line.

Current passing through the filter 204 and amplified, if necessary, causes the operation of relay 2II. This relay 2II operates common relay 2I8 and also relay 2I9. Relay 2I9 locks in a circuit from battery through its winding and left contact, through the make-before-break contact of relay 2I8 to ground at the back contact of relay 220. Relay 2I9 at its right contact connects ground over conductor 22l through a contact of relay 300, Fig. 5, to battery through the left-hand winding of relay 302. Relay 302 operates to register the digit and prepares to lock in a circuit which will be described presently. When the key I06 is released by the subscriber, contacts H8, H1 and H8 restore to normal and the generator I00 is removed from the line circuit. Current therefore ceases to flow in the filter circuit 204 and relay 2II releases, in turn releasing relay 2| 8. Relay 2I8 in releasing, closes its normal contacts before opening its front contacts. Therefore, before the locking circuit of relay M9 is opened to permit the release of this relay, a holding circuit is closed as follows for the register relay 302; battery through the right winding and contacts of relay 302, winding of relay 303, right normal contacts of relays 304, 305 and 306, conductor 301, normal contacts of relay 2 I8 to ground at the contact of relay 220. Relay 302 looks in this circuit and relay 303 operates. When relay 2I8 fully releases, it opens the locking circuit of relay 2I9, and the latter relay releases. Relay 303 releases relay 300 to disconnect the common leads 30l from register A. Relay 303 also closes an operating circuit for relay 304. This circuit may be traced from battery through the winding of relay 304, normal left contact of relay 308 to ground at the contacts of relay 303. Relay 304 operates and extends the leads 30I through to the register B. The operated register relay 302 and relay 303 are now held in a circuit extending to ground through the front contacts of relay 303. The equipment is now in readiness for the receipt of the second digit of the called designation.

When the subscriber manipulates key I09 to transmit the second letter L, the condenser I54 is connected in the circuit in the same manner as was condenser I5I upon the actuation of key I06 and the generator I00 is introduced into the line circuit. The connection of condenser I54 in the line circuit causes a different one of the frequencies generated by the device I00 to be selected and transmitted over the line circuit to the central office. This frequency characterizes the digit 5, or the letter L of the assumed designation and is passed by the selective network 201 and relays 222, 223 and 2I8 operate. Relay 223 looks as above described and applies ground to the common conductor 224, which now extends through the corresponding contact of relay 304 to operate the register relay 309 of register B. When the subscriber releases the key I09, the generator I00 is removed from the circuit and the relays 222 and 2I8 release. Relay 2I8 in releasing closes a locking circuit for relay 309 traceable from the right winding and contact of said relay, winding of relay 308, thence as previously traced over conductor 301 to ground. Relay 309 looks and relay 308 operates in this circuit before the holding circuit of relay 223 is broken. On the full release of relay 2I8, the holding circuit of relay 223 is open and the latter relay releases. Relay 308 in operating causes the release of relay 304 to disconnect the leads from the register 13. Relay 308 also closes an obvious circuit for the operation of relay 305 which extends the leads .30I through to the relays of the thousands registers Th. The operated register relay 309 and relay 308 now hold in a circuit extending to ground through the right contacts of relay 308.

In a similar manner the depression of the keys corresponding to the four numerical digits causes the operation of relays of the thousands, hundreds, tens and units registers. The depression of key I05 for the thousands digit I produces a current of a definite frequency in the common circuit 2I8 which is passed by the filter 203 to cause the ultimate operation of register relay 3I0 of the thousands register. The actuation of key I08 for the hundreds digit 2 causes the operation of a relay in' the hundreds register corresponding to the relay 3 of the thousands register. The manipulation of key I0I for the tens digit 3 produces a current of definite frequency in the common circuit 2 I 6 which is passed by the filter 205. Relay 230 thereupon operates causing relay 23I to operate and apply ground potential to conductors HI and 232 leading to the tens register. This results in the operation of two relays of the tens register corresponding to relays 3I0 and 3 of the thousands register. Finally the actuation of key I08 for the units digit 4 causes the operation of units register relay 3I2.

In a manner well known in the art and as fully disclosed in the hereinbefore-identified Raymond et a1. patent, the operated register relays now serve to control the selective operations of the switches S, 8-2 and S3 to complete the extension of the calling line through to the called line 208. Thereafter, the register sender is restored to normal and the parties converse with each other. At the end of conversation release of the switching equipment takes place in the well-known manner.

What is claimed is:

1. The combination in a signaling system of aline having a station thereon, a source of alternating current of a given frequency at a central oflice, means for connecting said source to said line to supply current thereto, a harmonic generator at said station responsive to current from said source to generate harmonics of the base frequency in said line, means at the central office selectively responsive to the harmonics generated at said station, and means at said station for selecting the generated harmonics for transmission to the central omce.

2. The combination in a signaling system of a line having a station thereon, a source of alternating current of a given frequency at a central omce, means for connecting said source to the line to apply current thereto, means at said station responsive to current from said source to generate harmonics of the given frequency and reflect them into said line, means controlled by the subscriber at said station for causing certain of the generated harmonics to be successively transmitted to said central oflice to characterize the characters of a telephone designation, and means at said central ofiice selectively responsive to the transmitted harmonics.

3. The combination in a signaling system of Q5 a line having astation thereon, a source of alternatlng current of a given frequency at a central oflice, means r p nsive to the initiation or a call at said station for connecting said source to said line, a'designation sender. at said station.

a coil atsaid stationzhavinga core material of very high permeability-at-lowmagnetizinz forces and which saturates at reiatively-1owflelds,;means at saidstation-ior introducing said-coil into said rea'ctance associated -.with said generator. manu'ally operated'means at said station for includingvariabie amounts of said reactance in circuit with said generator to variably time said tuning linejcircuit to the excited by current from said source and generate harmon'ics-M the givenjireuency, said means tunctioningto introduce intosaiddine circuit-other means for selectinga particular on'egof the gene'rated bar-. monies and cause it to to the central ofllce, and means at the central .oflice se-' 1 lectively responsive to the. transmittedharmonim '4."1 'he combinationj'in a asigna-iing-system of a line having v a station thereon, 1 asource offalteri nating current of a given frequency at a central omce, means responsive, to a the initiation 'of a call at said station for connecting said source to said line, a h armon1c -,snerator;at said station responsive to current from ,said source for gencrating harmonics of the given frequency, a T iundamentai frequency, selecting the generated "harmonics in a manner to characterize the characters of the telephone designation, trans- .fimitting the selected harmonics to said first point tuned circuit for each of a given number of the generated harmonics, and means at. said station for repeatedlvconnectingwsaid generator to said line andforisuccessiveiyiassociating sald tuned circuits withsaid 'line' to cause corresponding harmonics tobe selected and transmitted-tosa'id I centr'al omce, and means at said central omce ultaneouslyf';

selectively responsive to the transmitted harmonies.

5. The combination in a telephone system of a line having a stationthereon, a source of ai- :ternating current and means tor-connecting the same'to'said line, a harmonic generator at said station responsive to current trom'said .source circuit to the frequencies generated by said harmonic generator, means for coupling said tuning .,circuit' to said line to produce in the line currents'having trequencies' determined by said -v'ariable reactance, and means controlled by the currents in said line for registering the designations ot telephone subscribers.

@1- 6; The method of transmitting telephone designations from one point to another which com- ;Tprises vgenerating at one point a fundamental frequency, utilizing the fundamental frequency at the ;othe'r. point to. generate harmonics of the and registering them thereat. ROBERT c; MATHES. 

